1. Field of the Invention
This invention relates to a hand tool for determining the radius of a rounded corner on a workpiece.
2. Description of the Prior Art
Very few means are available today for assessing the radius of a convex surface on a workpiece. Such a measurement is of extreme importance, for example, during rebuilding when it is necessary to precisely match a curved surface with an identical surface on a new part. Such rebuilding is commonly undertaken when constructing a tool and die set so that the stampings produced from the new die set dimensionally conform to the stampings made by the old die set.
In the past, the radius of a convex surface has typically been obtained by use of a set of precision ground, sheet metal radius gauges. The radius is determined, through trial and error, by placing each of the curved gauges against the curved surface until a gauge is found that visually fits the surface and best precludes the passage of light between the gauge and the workpiece. Unfortunately, such sheet metal gauges are very expensive. Furthermore, the gauges by necessity are available only in discrete increments and thus the exact radius of the workpiece surface, when not identical to one of the gauges, cannot be found.
As an alternative to the commercially available sheet metal radius gauges, the machinist may opt to fabricate a curved template, again using a trial and error technique, until a finished template is produced that provides a close, visual fit to the workpiece. However, such a technique is necessarily time consuming and the finished template is useless for subsequent determinations involving different radii. Furthermore, no practical means exist for quickly checking the accuracy of the final determination.
Several devices have been proposed in the past for gauging a radius of curvature. For example, U.S. Pat. No. 3,217,418 to Wennerberg discloses a device which determines the radius of curvature on an article wherein the location of the centers of such curvatures are known from a blueprint or other design information. Unfortunately, such information is often not available to the machinist when constructing new parts to match the old parts.
In U.S. Pat. No. 2,796,671 to Aller, a radius gauging device has a swingable arm which is movable to contact an internal, concave surface of a bearing ring race. The arm is also shiftable to a point wherein the pivot axis and the curvature center coincide, such that the radius of curvature can apparently be determined. However, the device is not suitable for determining the radius of a convex surface and the device cannot be used on a workpiece that does not have a generally circular outer surface.